472 



THE JURASSIC PERIOD 



very lightly constructed, and set at right angles with the neck, as 

 in birds. In the Jurassic species the jaws are more or less com- 

 pletely armed with teeth, which by their form show the carnivo- 

 rous propensities of the animal. The joints of the external or 

 little finger of the hand are much thickened and elongated, this 

 finger being longer than the body and legs together. A mem- 

 brane, or patagium, was stretched between the elongate finger 

 on one side, and the body and leg on the other, thus forming the 



wing, which rather resembled the 

 wing of the bat than that of a bird, 

 though differing from the former in being 

 supported by one finger instead of four. A 

 few exceptionally well preserved specimens 

 found in the Solenhofen limestones have 

 retained the clearly-marked impressions of 

 these wing membranes. The legs, like those 

 of bats, were small and weak, and the tail 

 was. very short in some species, very long 

 in others. Some, at least, of the latter had 

 a membranous, oar-like expansion at the 

 tip of the tail. That the Pterosaurs had 

 the power of true flight, and did not merely 

 take great leaps like the flying squirrels, 

 is shown by the hollow, pneumatic bones 

 (like those of birds), and by the keel on the breast-bone for the 

 attachment of the great muscles of flight. This keel is found in 

 both birds and bats. The skin was naked, having neither scales 

 nor feathers. The Jurassic Pterosaurs were small, the spread of 

 wings not exceeding 3 feet. 



Birds. — One of the most remarkable advances which Jurassic 

 life has to show consists in the first appearance of the birds. As 

 yet, only a single kind of Jurassic bird has been found, and that 

 in the Solenhofen limestones. This, the most ancient known bird, 



Fig. 157. — Restoration 

 of Pterosaurian, Rham- 

 phorhynchus. (Zittel.) 



